Programmatic advertising has revolutionized digital marketing, allowing advertisers to reach the right audience at scale and in real-time. But with this rapid automation comes a complex web of intermediaries—Demand-Side Platforms (DSPs), Supply-Side Platforms (SSPs), ad exchanges, resellers, and publishers—all playing a role in the journey of a single ad.
While this ecosystem enables efficiency and precision targeting, it also creates opportunities for fraud, hidden fees, and unauthorized inventory reselling. Without visibility into the supply chain, advertisers risk buying ad placements on low-quality or fraudulent websites, and publishers may not get paid fairly for their inventory.
In any industry with multiple middlemen, transparency is key. Just like in retail, where brands need to ensure their products reach consumers through authorized distributors, advertisers need to verify that their ads are served on legitimate inventory. Without clear oversight, fraudulent players can exploit the system, leading to wasted ad spend and revenue losses.
To address these challenges, the IAB Tech Lab introduced ads.txt and sellers.json—two essential tools that help verify inventory sources, prevent fraud, and improve transparency in the programmatic supply chain.
What is Ads.txt?
Authorized Digital Sellers (ads.txt) is a standard that allows publishers to list authorized sellers of their ad inventory. This publicly accessible file, hosted on a publisher’s website, helps buyers verify that they are purchasing legitimate ad inventory and prevents domain spoofing.
Here’s an example of what an ads.txt file might look like:
datawrkz.com, 12347990, DIRECT
google.com, pub-1234, RESELLER
DIRECT means the publisher has a direct relationship with the seller.
RESELLER indicates the seller is authorized to resell the inventory.
For mobile apps and Connected TV (CTV), a variation called app-ads.txt does the same job, ensuring transparency in in-app advertising.
What is Sellers.json?
Sellers.json is another initiative by the IAB Tech Lab that works alongside ads.txt. While ads.txt helps advertisers verify sellers, sellers.json helps identify who is involved in selling ad inventory.
Maintained by SSPs and ad exchanges, sellers.json provides details on:
- The seller’s name
- Their domain
- Whether they are a publisher, intermediary, or reseller
If there’s a mismatch between a seller’s ads.txt entry and the corresponding sellers.json record, it could indicate unauthorized reselling or fraud.
How Ads.txt and Sellers.json Work Together
Ads.txt and sellers.json complement each other to create a more transparent ad supply chain:
1. Ads.txt (Publisher’s Side) – Publishers list authorized sellers of their inventory.
2. Sellers.json (Platform’s Side) – SSPs and exchanges provide a directory of sellers involved in transactions.
3. SupplyChain Object (schain) – This tracks every entity in the supply chain to ensure transparency at each step.
For example, when a bid request is made:
- The SSP checks ads.txt to confirm the seller is authorized
- The SSP then adds its identifier in the supply chain (schain object)
- Advertisers can cross-check this data with sellers.json to verify legitimacy
Why Supply Chain Transparency Matters
Without these tools, the digital ad space would be like a marketplace with no regulations—anyone could claim to sell premium inventory, leading to:
-Ad fraud: Fake publishers selling fraudulent impressions
-Hidden fees: Unnecessary middlemen taking a cut
-Brand safety risks: Ads appearing on unsuitable or low-quality sites
By using ads.txt and sellers.json, the industry benefits from:
-Fraud Prevention – Protects against domain spoofing and unauthorized reselling
-Better Transparency – Advertisers can track exactly where their ad spend is going
-Higher Efficiency – Reduces intermediaries, leading to better cost efficiency
-Stronger Brand Safety – Ensures ads appear only on approved, high-quality inventory
Why Transparency Can’t Be Ignored
Supply chain transparency isn’t just a best practice—it’s essential for a safer, more efficient digital advertising ecosystem. When advertisers, publishers, and platforms embrace ads.txt and sellers.json, they create a trustworthy and fraud-resistant marketplace.
For advertisers, this means knowing where your ads are running. For publishers, it ensures fair compensation for your inventory. And for the industry as a whole, it brings accountability and efficiency to programmatic advertising.
By implementing these tools correctly, media owners and advertisers can minimize fraud, optimize ad spend, and build a transparent programmatic ecosystem.
